The present invention relates to systems (method and apparatus) for confocal microscopy for the examination or imaging of sections of a specimen of biological tissue, and particularly to such systems using multi-spectral illumination and processing of multi-spectral light.
Medical imaging technology has advanced over the last twenty years to provide physicians with indispensable information on the macroscopic anatomy of patients. Imaging techniques such as radiography, magnetic resonance imaging, computed tomography, and ultrasound non-invasively allow investigation of large-scale structures in the human body with resolutions ranging from 100 xcexcm to 1 mm. However, many disease processes, such as the detection of early stages of cancer, higher resolution is necessary for proper diagnosis. In addition, clinical procedures such as screening for carcinoma and the surgical detection of tumor margins require higher resolution diagnostic imaging methods.
To address these and other clinical problems in situ, a non-invasive imaging technology with a resolution that approaches standard histopathology must be used. One promising potential noninvasive imaging modality is a form of light microscopy known as reflectance confocal microscopy.
Currently, the use of fast scanning confocal microscopy is limited to accessible surfaces of the skin and the eye. The reason for this is that the only reliable methods for optical scanning must be performed in free space. In addition, the size of these optical scanners prohibit their use in small probes such as endoscopes or catheters. It is a feature of the invention to miniaturize the fast scanning mechanism and increase the number of medical applications of confocal microscopy to include all surfaces of the body, gynecologic applications, probe-based applications, and internal organ systems.
Multi-spectral light was proposed for use in confocal microscopy, but only for imaging vertically-spaced regions of a body under examination. See B. Picard, U.S. Pat. No. 4,965,441, issued Oct. 25, 1990. An interferometer using a grating to obtain multi-spectral light which is resolved in the interferometer to obtain a spectroscopic image is disclosed in A. Knuttal, U.S. Pat. No. 5,565,986, issued Oct. 15, 1996. A lens having a color separation grating which obtains a multi-spectral light is disclosed in U.S. Pat. No. 5,600,486, issued Feb. 4, 1997. Such multi-spectral proposals are not effective for high resolution imaging using a compact, flexible probe. A confocal microscope system according to this invention can be miniaturized and incorporated into a compact probe. In addition, by allowing light delivery through a single optical fiber, the probe may also be easily incorporated into catheters or endoscopes. Thus, a confocal microscope in accordance with the invention allows imaging of all accessible surfaces of the body and increases the biomedical applications of confocal microscopy by an order of magnitude.
Briefly described, a confocal microscopy system embodying the invention illuminates a region of interest in a body into which said probe may be inserted with a confocal spectrum extending along one dimension. Optics in said probe or physical movement of said probe enabled by attachment thereto of a flexible light conductive member (which may be an optical fiber), enables scanning of said spectrum along one or two additional dimensions thereby providing for two or three dimensional imaging of the region. The reflected confocal spectrum may be detected or decoded spectroscopically, preferably with a heterodyne detection mechanism which may be implemented interferometrically.
The following are hereby incorporated by reference:
Corcuff, P. and J. L. Leveque, In vivo vision of the human skin with the tandem scanning microscope. Dermatology, 1993. 186: p. 50-54;
Rajadhyaksha, M., et al., In vivo confocal scanning laser microscopy of human skin: Melanin provides strong contest. J. Invest. Derm., 1995. 104: p. 946;
Webb, R. H., Scanning laser ophthalmoscope, in Noninvasive diagnostic techniques in ophthalmology, B. R. Masters, Editor. 1990, Springer-Verlag: New York; and
Tearney, G. J., R. H. Webb, and B. E. Bouma, Spectrally encoded confocal microscopy. Optics Letters, 1998. 23(15): p. 1152-1154.
In order to image the majority of accessible epithelial tissues in vivo three important requirements must be met. First, a focused beam must be scanned across the specimen. Second, the image acquisition time has to be sufficiently short to prevent motion artifacts. Finally, the device must be small enough to be incorporated into and endoscope or catheter. Techniques such as tandem scanning and laser scanning confocal microscopy have been developed address the rapid beam scanning requirements for an in vivo confocal imaging system. However, in these methods, high speed scanning is obtained through the use of large mechanical devices that are not easily miniaturized. As a result, the utility of these techniques is primarily limited to the fields of dermatology and ophthalmology. A promising new a fiber optic based technique, spectrally encoded confocal microscopy (xe2x80x9cSECMxe2x80x9d), has recently been demonstrated. This technique allows reflectance confocal microscopy to be performed through a compact probe, such as a catheter or endoscope. SECM uses wavelength division multiplexing (xe2x80x9cWDMxe2x80x9d) to encode one-dimensional spatial information reflected from the sample. The fast scanning axis is replaced by a series of focused points with each location being represented by a different wavelength of light. The remittance as a function of spatial position is determined by measuring the spectrum of the reflected light (FIG. 8). A two-dimensional image is created by scanning the wavelength-encoded axis by slow mechanical motion of the probe. Thus, endoscopic devices embodying the invention allow SECM imaging of a variety of tissues and organs either integrated with standard endoscopes or as stand-alone devices.
In accordance with an embodiment of the invention, a device capable of performing in vivo endoscopic confocal microscopy is provided. Such a device could potentially provide physicians with a tool for performing non-invasive subcellular diagnostic imaging in internal organ systems. Such a modality would have significant long-term impact in its ability to enable a variety of clinical applications including cancer screening or biopsy guidance and intraoperative tumor or other tissue identification. A device embodying the present invention could enable in vivo endoscopic confocal microscopy imaging and potentially allow diagnosis of critical tissues of interest. Despite the added complexity, such a device could provide access to otherwise inaccessible tissues therefore significantly enhancing the value of confocal microscopy as a diagnostic tool.